#include <stdio.h>
#include <malloc.h>

int main(void)
{
    {
        void* p1 = malloc(1);
        size_t s = malloc_usable_size(p1);
        printf("usable size: %ld\n", s);
        free(p1);
    }

    {
        void* p1 = malloc(200<<10);
        size_t s = malloc_usable_size(p1);
        printf("usable size: %ld\n", s);
        free(p1);
    }
}